JP2000186992A - Viscosity determining method in density measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a viscosity determining method in correcting the density of a specimen based on viscosity. SOLUTION: In this viscosity determining method, viscosity is determined by determining to which region of a peak point a damping coefficient acquired in a frequency of a specific degree belongs based on whether or not, when either a viscosity-damping coefficient characteristic of a specimen in a specific degree of vibration has the peak point, or a viscosity-damping coefficient characteristic of the specimen in other specific vibration is larger than the damping coefficient corresponding to the peak point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining a viscosity when correcting the density of a test substance based on the viscosity in a density measurement using a vibratory densitometer.

[0002]

2. Description of the Related Art A test substance (liquid or gas) is filled in a U-shaped tube having a fixed base end (upper ends of a U-shaped portion) and mechanical vibration is applied to the U-shaped tube. When given, the vibration is generated at a frequency corresponding to the density of the test substance filled in the U-shaped tube.
Vibrate . Therefore, the vibration frequency (or vibration cycle)
Is measured, the density of the test substance can be obtained. The vibrating density meter is based on this principle.

FIG. 2 shows a basic configuration of a conventional vibratory density meter. Tip of U-shaped tube 10 (lower part of U-shape)
The U-shaped tube 10 is vibrated by applying a current of a predetermined frequency to a drive coil 14 disposed near the permanent magnet. The vibration of the U-tube 10 is detected by a sensor 13, and a detection signal from the sensor 13 is amplified by an amplifier 12 and returned to a drive coil 14. With this configuration, the U-shaped tube resonates with the frequency of the current flowing through the drive coil and vibrates.
Further, based on the output signal from the sensor 13, the vibration cycle of the U-shaped tube is measured, and is used for the density calculation by the calculation means 15.

In the meantime, in the density simply obtained from the vibration frequency as described above, a density error depending on the viscosity of the test substance occurs as shown in FIG. That is, as the viscosity η increases, the error rate indicated by Δρ / ρ ₁ in FIG. 4 increases (when the true density value is ρ ₀ and the measured value is ρ ₁ , Δρ =
ρ ₁ −ρ ₀ ).

In order to correct the density error depending on the viscosity η, it is necessary to determine the viscosity of the test substance. Here, the viscosity η can be obtained from the relationship with the above-mentioned vibration damping constant. TRANSACTIONAL ON INDUSTRIAL ELECTRONICS
AND CONTROL INSTRUMENTATION, VOL.IEC1-27, NO.3, AUGU
ST 1980, 247-253 (Reference 1). That is, for example, the viscosity-damping constant characteristics are shown in FIG.
The functions are represented by b0 = f (η) and b1 = g (η). Here, the 0th-order oscillation is a mode in which the base end of the U-shaped tube has a node of vibration as indicated by i = 1 in FIG.
Usually, the density is determined from the frequency in this mode. The primary vibration is a vibration having a node at a position from the base end and about 1/4 from the end as shown by i = 2 in FIG. In addition, higher order vibration modes (i = 3, i =
There is also 4).

[0006] In order to form the vibration of each mode described above,
The above document 1 is configured to be driven by a circuit as shown in FIG.

That is, the piezoelectric element 21 as a sensor
Of the modulator 2 as a signal U via a variable gain amplifier 22 and a voltage control phase adjuster 23.
4 and input to the phase shifter 25.

Further, the signal U is supplied to the rectifier 26 and the integrator 2
7, a control signal Uc of the variable gain amplifier 22 is formed. The loop of the variable gain amplifier 22 → the voltage control phase adjuster 23 → the rectifier 26 → the integrator 27 → the variable gain amplifier 22 has a function of making the magnitude of the output U constant regardless of the magnitude of the detection voltage.

The modulator 24 outputs a value obtained by multiplying the amplitude of the basic signal U by a modulation coefficient ε.
Reference numeral 5 outputs a signal obtained by shifting the phase of the basic signal U by -θ (for example, 45 °). The two signals are added together by the mixer 28 to obtain a signal Ue whose phase is shifted by an amount corresponding to the magnitude of the modulation coefficient ε, as shown in FIG. Iexc. That is, the signal U is converted to the phase shifter 25
And the coefficient ε ₁ or ε
_The signals ε ₁ U and ε ₂ U multiplied by ₂ (in FIG. 8, ε ₁ >
Signals Ue ₁ and Ue _{2 obtained} by adding ε ₂ ) and basic signal U have a delay angle θ ₁ > θ ₂ when ε ₁ > ε ₂ .

The modulation coefficient ε can be changed by adjusting the value of N of the control signal ω / N input to the modulator 24.

When the phase-shifted signal is obtained as described above, a resonance frequency at a new phase is naturally obtained, and the first harmonic, ie, vibration of i = 2 or higher order vibration can be obtained. Become.

When the relationship between the viscosity and the damping constant is actually measured by the above-described apparatus with the zero-order vibration, as shown in FIG. 3A, and when the relationship is measured with the first-order vibration, the relationship shown in FIG. Like
FIG. 5 shows the two graphs superimposed.

Here, assuming that the viscosity-damping constant characteristic b0 = f (η) at the time of the zero-order vibration is used to correct the density error due to the viscosity of the density, the viscosity η ₁ (specifically, About 100 mPas), the attenuation constant has a peak,
It will have two viscosities for the same damping constant, and it will be a problem which value to use. When the first-order viscosity-decay constant characteristic b1 = g (η) is used, the viscosity can be uniquely obtained from the damping constant over a relatively wide range, but the viscosity peaks at the portion of the viscosity η ₂ (about 700 mPas). Therefore, the same problem as in the case of using the zero-order vibration is encountered.

For a substance whose viscosity can be predicted to be about 700 mPas or less, the viscosity obtained from the first-order vibration can be used. The method of correcting the density error using the viscosity obtained from the vibration has a disadvantage that high accuracy cannot be expected.

The present invention has been proposed in view of the above-mentioned conventional circumstances. Even when a specific order of vibration has a peak in the viscosity-damping constant characteristic, another specific order of viscosity- It is an object of the present invention to provide a method for determining the viscosity in the vibration of the specific order by using the damping constant characteristic.

[0016]

In order to achieve the above object, the present invention employs the following means. In other words, when the viscosity-decay constant characteristic of the test substance in a specific order vibration has a peak point, whether the damping constant of the test substance in another specific order vibration is larger than the value corresponding to the peak point. The viscosity is determined by judging to which region of the peak point the damping constant obtained at the specific order frequency belongs based on whether it is small.

If the 0th order used directly for density measurement is used as the specific order and the 1st order is used as the other specific order, viscosity measurement can also be performed in a vibration mode used for density measurement, thereby improving accuracy. Can be expected.

[0018]

FIG. 1 is a diagram showing an outline of the present invention.

[0019] similar to that shown in FIG. 5, when driven by changing the viscosity of the test substance U-tube vibratory densitometer at 0-order mode, the viscosity having peaks in viscosity eta = eta ₁ - attenuation constant The curve b0 = f (η) is obtained. When trying to obtain the viscosity of the test substance having the attenuation constant f (η ₀ ) using this curve,
The viscosity will have two values, η ₁₀ and η ₂₀ .

Therefore, a viscosity-decay constant curve b1 = g (η) is obtained by changing the viscosity by using the first-order vibration mode in addition to the viscosity-decay constant curve by the zero-order vibration mode. The viscosity - the attenuation constant curve b1 = g (η), the attenuation constant which corresponds to the viscosity _{η = η 1 g (η 1} )
Becomes Therefore, the viscosity-decay constant curve b0 = f
Two viscosities η obtained from the damping constant f (η ₀ ) of (η)
Which of the values of ₁₀ and η ₂₀ is to be adopted can be determined depending on whether the attenuation constant g (η) in the first-order drive mode is larger or smaller than g (η ₁ ). That is, the attenuation constant g
When (η) is larger than g (η ₁ ), the viscosity η ₂₀ on the right side of the peak is obtained, and when the damping constant g (η) is smaller than g (η ₁ ), the viscosity η _{10 on} the left side of the peak is obtained. Value.

In the above description, the use of the first-order viscosity-decay constant curve b1 = g (η) when determining the viscosity from the zero-order viscosity-decay constant curve b0 = f (η) has been described. However, in the same way, when determining the viscosity from the first-order viscosity-decay constant curve b1 = g (.eta.), The zero-order viscosity-decay constant curve b0 = f (.eta.) Can be used.

That is, a first-order viscosity-decay constant curve b1
= G (η) peaks near the viscosity η ₂ and the viscosity η ₁
The curve shows two viscosities for the same damping constant from around the point where. Therefore, the damping constant g (η ₀ )
Which one of the two viscosities η ₃₀ and η ₄₀ obtained from the above is adopted is determined by a viscosity-decay constant curve b0 =
Judge from f (η). That is, 0-order viscosity for the same analyte - attenuation constant curve b0 = f (η) from the resulting attenuation constant f (eta) is f (η ₂₎ left viscosity eta ₃₀ peaks when larger, but also , The damping constant f (η) is f
When it is smaller than (η ₂ ), the viscosity η ₄₀ on the right side of the peak should be obtained.

For example, the 0-order vibration causes the U-tube 10
Is oscillating at a frequency of about 200-350Hz,
In the above first-order vibration, it is 6.2673 times the above-mentioned 0th-order vibration, which is approximately
It vibrates at a frequency of about 1253 to 2194 Hz, and the viscosity characteristics may change in these two frequency bands depending on the measurement object. On the other hand, the measurement of the density is currently performed using the 0th-order vibration having a large amplitude. Since the density measurement is performed by the 0th-order vibration, the viscosity causing the density error is also reduced to the 0th-order vibration. It can be expected that more accurate correction can be made by using the viscosity below.

Table 1 is a table summarizing experimental data from the above viewpoints. That is, for each of the viscosity standard solution (Sample A) [Newton substance] and Samples B to E, 0
The damping constant was measured for the next vibration and the first vibration, and FIG.
While obtaining the viscosity using the graphs (a) and (b) of (a) and (b), the density of each of the samples was measured by the 0th-order vibration. The corrected density is obtained by correcting the density obtained as described above with the viscosities obtained by the zero-order vibration and the first-order vibration, respectively, using the graph of FIG. 4 (or a specific formula).

When the corrected density obtained in this way is compared with the true value of the density (obtained by the Wardon pycnometer method), in particular, the substances of samples B to E are obtained from the zero-order vibration. It can be understood that the corrected density obtained using the obtained viscosity has much higher accuracy.

A liquid whose shear rate (shear rate) is proportional to shear stress (shear stress) is a liquid whose viscosity characteristics do not change depending on the frequency band. A non-Newtonian substance is a liquid such as a polymer substance whose shear rate (shear rate) is not proportional to shear stress (shear stress), and also a liquid whose viscosity characteristics do not change depending on the frequency band.

[0027]

[Table 1]

As described above, according to the present invention, even when the viscosity-damping constant characteristic of a specific order has a peak, that is, when the viscosity-damping constant has two viscosity values for a certain damping constant. Also, the viscosity can be determined using the viscosity-decay constant characteristics of other orders. In addition, the same order of vibration can be used for density measurement and viscosity measurement, and measurement accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing viscosity-decay constant characteristics in each mode for explaining the principle of the present invention.

FIG. 2 is a conceptual diagram of a vibratory density meter.

FIG. 3 is a graph showing a density error due to a viscosity in a zero-order vibration and a first-order vibration.

FIG. 4 is a graph in which the two graphs of FIG. 3 are collectively displayed.

FIG. 5 is a graph of viscosity-decay constant characteristics in each mode.

FIG. 6 is a diagram showing a model of a vibration mode of a U-shaped tube.

FIG. 7 is a conventional circuit diagram.

FIG. 8 is a waveform diagram showing a phase shift according to the related art.

Claims (2)

[Claims] 1. A method for determining a viscosity necessary for correcting a density error based on a viscosity of a test substance with respect to a measurement result of a vibration type densitometer, the method comprising: determining a viscosity of a test substance in vibration of a specific order; If the decay constant characteristic has a peak point, it is determined whether the decay constant measured using the viscosity-decay constant characteristic of the test substance at another specific order of vibration is larger or smaller than the decay constant corresponding to the peak point. Determining the viscosity by determining whether the viscosity obtained from the damping constant obtained by the vibration of the specific order belongs to a region larger or smaller than the peak. Viscosity determination method. 2. The method according to claim 1, wherein 0th order is used as the specific order, and 1st order is used as the other specific order.